Optimized state-discrimination receiver strategies for nonorthogonal states can improve the capacity of the communication channels operating with error rates below the ones corresponding to conventional receivers. Coherent signal-nulling receivers use a local oscillator to null the signal state and perform the discrimination of the signal from an alphabet of nonorthogonal states. We describe our study of signal nulling for signals encoded in nonorthogonal phase states. The signal nulling discrimination setup is the first step for the experimental investigation of different discrimination strategies for receivers of coherent multi-phase encoded signals.